Apparatus for making electron-emitting cathodes



Feb. 2, 1937. I E. w ci-i 2,069,637

US FOR MAKING ELECTRON EMITTING CATHODES Filed March 26, 1935 Patented Feb. 2, 1937 APPARATUS FOR MAKING ELECTRON-EMIT- TING CATHODES Edward H. Wittich, Emporium, Pa., assignor to Hygrade Sylvania Corporation, Salem, Mass., a corporation of Massachusetts Application March 26, 1935 Serial No. 13,107

10 Claims.

This invention relates to electron-emitters and more particularly to means for providing such emitters with their electron-emissive coatings.

Heretofore, electron-emissive coatings have been applied to filaments and cathode sleeves or the like by spraying or by the so-called cupping process, the latter process requiring the employment of a series of cups containing the coating material and through which the filament to be coated is successively passed. .The spray process however entails certain disadvantages, the most pronounced of which is the diificulty of securing uniformity of coating. This diificulty is further accentuated in connection with so-called indirectly heated cathodes employing a tubular metal sleeve, because the cupping process is not feasible as applied to this type of cathode, and resort must be had spraying. However, even when such cathode sleeves are sprayed, it is extremely diificult to control the uniformity of coating because of a number of factors requiring control including density of the spray, clogging of the spray-gun, different sizes of sleeves to be coated, andmaintenance of proper temperature, 5 humidity and cleanliness of the spray compartment. Ancillary to the above noted difiiculties is the waste of material during spraying, particularly when it is considered that the usual cathode sleeve is of relatively minute dimensions and in order to utilize the spray process it is'necessary to position the sleeve in a cloud of spray. Thus, the spray process ordinarily results in non-uniformity of coating not only along the. length and circumference .of each cathode, but even successively sprayed cathode sleeves will vary among themselves thus militating against the desired uniformity of operation in the finished tubes.

Accordingly one of the .principal objects of this invention is to provide a means to coat bodies \40 whether of the filamentary or tubular sleeve type,

whereby uniformity of electron-emissive coating is obtained.

In certain cases it is desirable to be able to provide a filament or cathode. sleeve with a coating which possesses a predetermined distribution of coating material. Thus it may be desired to provide the end regions of a filament or of a cathode sleeve with a thicker coating than the middle region, while maintaining the coatings in these respective regions uniform. Such a result is obviously unattainable with ordinary spray or cupping processes. l

Accordingly, another object of theinvention is to provide a means whereby the thickness as well as the uniformity of electron-emissive coating may be accurately controlled.

A feature of .the invention relates to a device for coating. cathodes wherein the coating is sub:

jected to centrifugal force to insure its uniformity and to prevent beading of the coating material.

Another feature relates to a machine for coating cathodes, whereby the boundaries of the electron-emissive coating can be sharply defined.

Another feature relates to a machine for coating cathodes which is adapted to automatic loading, coating and discharge of the coated cathodes thus insuring uniformity in large batches of the finished product.

Other features and advantages not specifically enumerated will be apparent'after a consideration of the following detailed descriptions and the appended claims. 7

While the invention will be disclosed herein as embodied in one particular form of machine and in connection with the coating of one known type of cathode, it will be understood that this is done merely for purposes of explanation and vnot'by way of limitation.

Accordingly, in the drawing Fig. 1 is a perspectiveview of .one preferred embodiment of the invention.

Fig. 2 is a detail sectional view of part of the mechanism of Fig. 1. 1

' Fig. 3 is a part sectional view of a modified form of coating roller.

Referring to Fig. 1, the numeral I indicates any suitable base upon which the various parts of the machine are supported. Afflxed to base I, for example by screw 2 is a standard lwhlch has bolted to it upper end a guidemembe'r 4 through which passes the vertical arm 5 of a cathode supporting frame. Preferably the arm 5 is rectangu lar in' cross section, and the bore of member 4 is likewise rectangular to prevent the frame turning while it is being reciprocated. The said frame is provided with a hollow arm '6 throughwhich passes the rotatable spindle I, the latter having attached to its right hand end a suitable pulley 8, the left hand end of the spindle being provided with a head 9. The head 9 is provided with an opening to receive and frictionally retain the member I0 to'be coated. Thus the head 9 may have fitted into the end thereof a rubber bushing into which the member It may be easily inserted and held in axial alignment with spindle I. The slidable frame is reciprocable vertically and is normally held in its lowered position by reason of spring H which has one end fastened '55 vide the end regions of the cathode sleeve with a thicker coating than the middle region.

In order to accomplish this result the coating roller instead of being provided with grooves of uniform cross-section may be provided with grooves of larger cross-section at the end. Such ll urges the frame downwardly so that the lower flrmller is"diagrammatically illustrated iLLFigrB end of arm 5 engages the inner end of lever l2, and when it is desired to raise the frame the outer end of said lever is lowered and may be held in its lowered position by means of a suitable catch Fastened to base I is another standard I having an arm II on which is supported a reservoir l8 containing the coating'material i! in liquid or semi-liquid form. An inlet pipe 20 supplies the coating material to the reservoir and an overflow'pipe 2| is provided to prevent the liquid rising above a predetermined level. Standard It supports a bearing member 22 in which rotates the spindle 23, said spindle having attached to its right-hand end the grooved roller 24 and at its left-hand end the pulley 25. The pulleys I and 25 may be driven from the continuously rotating shaft 25 through respective pulleys 21, 2| and belts 29, 30. Preferably the pulleys are designed so that the spindle I rotates at a higher speed than the spindle 23.

Any known type of electron-emissive coating liquid may be employed so long as the viscosity and level of the liquid in the reservoir II are chosen so as to give the desired thickness to the coating. Preferably, although not necessarily, the grooves in roller 24 are curved in cross-section but if desired these grooves may be V-shaped.- Preferably also the grooves are designed as regards their depth and width so that for a given viscosity of the coating liquid, there is a prede termined amount of the said liquid carried by the grooves as they emerge from the surface of the liquid. As the roller 24 rotates, due to the viscosity of the coating material, each groove carries with it an accurately predetermined amount of coating material, so that when the cathode sleeve is lowered into coating position as indicated in Fig. 2, the material in the grooves is uniformly applied to the sleeve. It will be noted that in order to effect the coating it is not necessary that the cathode sleeve be brought into physical contact with the surface of the roller, since the cathode sleeve is being rotated at relatively high speed and the centrifugal force tends to smooth out any irregularities or striations in When the required amount of material has been applied, the lever i2 is operated to raise the cathode which however continues to rotate until it is removed fromthe head 9. The coated cathode sleeve after being removed, may be dried or baked in any well known manner and then packed in suitable containers ready for ,In some types of electron-emitting devices it is desirable to provide a cathode sleeve with different thicknesses of coating at different parts of the sleeve. This of course is to be distinguished. from the'haphazard non-uniformity which results from the ordinary spraying or cupping processes. In such types of tubes it is required that the thickness of the coating (even though this thickness may vary along the length of the cathode) should be accurately controlled and should be uniform-in large batches of coated sleeves. Fbr example in some cases it may be desirableto proof the drawing--wherein-.it-willbeseen that the end grooves are larger than the grooves in the middle regions of the roller.- Consequently, as the roller rotates a larger quantity of coating material is carried by the outer grooves, resulting in the application of a heavier coating to the end portions of the cathode sleeve. It will be clear therefore that the coating on the cathode sleeve maybe given any desired and accurately controlled distribution of electron-emissive material, be correspondingly designing the shape and size of the grooves in the roller.

From the foregoing description, it will be seen that there is provided a device which is well suited to the .complete automatic coating of cathode sleeves. Thus the cathode sleeves may be automatically loaded into the head 9 by any suitable mechanical loading means (not shown) and the raising and lowering of each cathode sleeve into coating relation with the roller 24 may be automatically timed 'so that each sleeve is subjected to the same duration of coating. At the end of this coating period the cathode sleeve may be automatically discharged from the head I0 and carried by a suitable conveyor or the like to another station where it may be baked or heated.

Various changes and modifications may be made herein without departing from the spirit and scope of the invention.

,What I claim is: v

. 1. A machine for applying an electron-emissive coating to an electrode including a reservoir of coating material, a grooved roller partly immersedin said liquid, means for holding the electrode with its surface in proximity to said roller but spaced therefrom, and means for rotating said electrode and said roller at different rotational speeds to apply a uniform coating of said material to said electrode.

2. A machine according to claim 1 in which I the electrode is rotated at a higher speed than said roller.

3. A machine of the character described comprising a reciprocable support for holding an electrode to be coated, a reservoir containing electron-emissive coating material, a pluralgrooved roller, means to rotate said roller and said electrpde, and, means ...to reciprocate said support to hold said electrode in spaced coating relation with said roller.

4. A machine of the character described comprising a roller having a plurality of circumferential grooves, a reservoir containing material to provide an electron-emissive coating to an electrode-an inlet for said reservoir, a level control outlet for said reservoir, means to reciprocate said electrode relatively to said roller, and means to rotate said electrode while in engagement with the material in said grooves but in spaced relation to said roller.

5. A machine of the character described comprising means to hold a cathode sleeve to be coated, means to rotate said sleeve, a coating roller having a plurality of circumferential grooves, means to rotate said -roller to fill said grooves with coating material, and means to raise and lower said sleeve into spaced coating relation with said 6. In a machine of the character described including a grooved coating roller, a reservoir in which said roller rotates, means to rotate said roller, means to hold a cathode sleeve to be coated, means to bring said sleeve into coating engagement with the material of said grooves but spaced from said roller, and means to rotate said sleeve to cause the coating to be smoothed out by centrifugal force.

'7. In a machine of the character described, a standard, a rotatable head to receive a cathode sleeve, said head being mounted for reciprocating motion on said standard, a grooved coating roller carrying electron-emissive material, a lever for raising and lowering said head, and means to rotate simultaneously said head and said roller,

, said head being arranged to hold the cathode sleeve in spaced relation to the roller during coat- 8. A machine according to claim.7 in which said head and roller are rotated at different speeds'in the same direction.

9. In combination, a grooved roller for applying a coating of liquid electron-emissive material to a cathode sleeve, and means to rotate the coated sleeve at sumciently high speed to smooth out said coatingby centrifugal force.

10. Means for applying to an electrode a coating of electron-emissive material and regulating the thiclmess of said coating at difierent regions of the electrode including a reservoir of coating material, a roller having a plurality of circumferential grooves certain of said grooves being larger than others, means for rotating said roller in said reservoir, and means for" bringing the electrode into spaced coating relation with the material in said grooves.

EDWARD H. WITTICH. 

